The present invention relates to a polarizer device and, more particularly, to a broadband microwave polarizer device capable of introducing a relatively constant differential phase shift between orthogonal components of input signals over a wide frequency bandwidth.
Microwave polarizer devices for introducing phase shifts between orthogonal components of signals are well known to those skilled in the art. For example, polarizer devices have been constructed using either pins, ridges or thin dielectric vanes (e.g., of "Teflon") within square or circular sections of waveguide, or by using sections of waveguide which are not circular or square, such as elliptical or slightly non-square sections of waveguide. In the case of pin-type polarizer devices, a pair of opposing rows of spaced-apart pins are normally arranged in a common plane in a section of waveguide and the phase shift introduced thereby may be approximated by EQU .phi..sub.p = A.sub.0 + A.sub.1 (f-f.sub.0) + A.sub.2 (f-f.sub.0).sup.2,
where f is the frequency of input signals applied to the polarizer device, f.sub.0 is the center frequency of the operating range of frequencies (bandwidth) of the polarizer device, and A.sub.0, A.sub.1 and A.sub.2 are constants, the values of which are determined by such factors as the number, cross section, depth and spacing of the pins. In a similar fashion, in the case of ridge-type polarizer devices, a pair of elongated opposing ridges are normally arranged in a common plane in a section of waveguide and the phase shift introduced thereby may be approximated by EQU .phi..sub.r = B.sub.0 + B.sub.1 (f-f.sub.0) + B.sub.2 (f-f.sub.0).sup.2,
where f is the frequency of input signals applied to the polarizer device, f.sub.0 is the center frequency of the operating range of frequencies of the polarizer device, and B.sub.0, B.sub.1 and b.sub.2 are constants, the values of which are determined by such factors as the depth, shape and thickness of the ridges.
In the design of a pin-type polarizer device as described above, it is generally desirable to make all of the constants except A.sub.0 as small as possible so that the phase shift introduced by the polarizer device does not vary significantly over the entire bandwidth. This result may be accomplished by making the value of the constant A.sub.1 equal to 0, for example, by the appropriate selection of characteristics for the pins of the polarizer device. However, although the value of the constant A.sub.1 may be made equal to 0, it is difficult at the same time to make the value of the constant A.sub.2 small. As a result, the phase shift introduced by the pin-type polarizer over the entire frequency bandwidth varies excessively, for example, by several degrees. In a similar fashion, it is difficult to control the values of the constants B.sub.0, B.sub.1 and B.sub.2 for a ridge-type polarizer device, with the result that the phase shift introduced by the polarizer device also varies by several degrees over the entire frequency bandwidth of the polarizer device. The aforementioned elliptical or slightly non-square waveguides also introduce phase shifts which vary by several degrees over the entire frequency bandwidth.